parent with autmatic weights giving wierd reults
This is a "think outside the box" kind of approach, but consider giving it a try, just to see what happens. No guarantees, of course (and truly, I'm sorry that I wasn't able to address the specifics of your problem more directly). Consider taking the source file, and NOT exporting anything. Start with that file, and instead of trying to extract anything from it, consider using it as is, BUT import your preferred model INTO that file. Once your model is in the source file, with the source file model selected, go into the object data tab in the Properties Panel and change the mesh data block to the one from your newly imported mesh. It MAY replace the source file's mesh with your desired mesh. If it does, then you would essentially have what you want, without doing a lot of work. You could then hide or delete your imported version of the mesh. Please let me know if this works. If not, maybe someone could tell us both why, and how to do what I'm suggesting properly.